Endodontic instrument having notched cutting surfaces

ABSTRACT

A fluteless endodontic file is provided, formed from a tapered shaft of material having a prismatic shape generally defined by three or more side surfaces and three or more interposed corners. A plurality of notches are cut into one or more corners defining cutting surfaces, points and/or edges. The notched cutting surfaces are formed such that the file, when rotated and/or reciprocated within a root canal, effectively cuts/debrides hard tissue (known in the art as dentin) as well as soft tissue, thus, forming an optimal canal shape. The cutting surfaces are also preferably formed at an angle to the centerline of the instrument to provide optimal cutting efficiency and material removal. The fluteless file design exhibits increased efficacy, with less tendency to bind and break within the root canal and also significantly reduces manufacturing and capital equipment costs.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120(e) to provisionalapplication Ser. No. 60/312,823 filed Aug. 16, 2001, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of dentistry andmore particularly to a fluteless endodontic instrument having notchedcutting surfaces for cleaning and enlarging a root canal.

2. Description of the Related Art

In the field of endodontics, one of the most important and delicateprocedures is that of cleaning or extirpating a root canal to provide aproperly dimensioned cavity while essentially maintaining the centralaxis of the canal. This step is important in order to enable completefilling of the canal without any voids and in a manner which preventsthe entrapment of noxious tissue in the canal as the canal is beingfilled.

In a root canal procedure, the dentist removes injured tissue and debrisfrom the canal prior to filling the canal with an inert fillingmaterial. In performing this procedure the dentist must gain access tothe entire canal, shaping it as necessary. But root canals normally arevery small in diameter, and they are usually quite curved. It istherefore very difficult to gain access to the full length of a rootcanal.

Many tools have been designed to perform the difficult task of cleaningand shaping root canals. Historically, dentists have used a widemultitude of tools to remove the soft and hard tissues of the rootcanal. These tools, usually called endodontic files, have been made bythree basic processes. In one process, a file is have been made by threebasic processes. In one process, a file is created by twisting aprismatic rod of either square or triangular cross section in order tocreate a file with helical cutting/abrading edges (“K-file”). The secondprocess involves grinding helical flutes into a circular or tapered rodto create a file with one or more helical cutting edges (“Hedstromfile”). The third method involves “hacking” or rapidly striking acircular or tapered rod with a blade at a given angle along the lengthof the rod, thus creating an endodontic file characterized by aplurality of burr-like barbs or cutting edge projections (“barbed file”or “broach”). Each of these methods produces an instrument having uniqueattributes, advantages, and disadvantages.

Endodontic files have historically been made from stainless steel, butdue to the inherent stiffness and brittleness of steel, these tools cansometimes pose a significant danger of breakage in the curved rootcanal. More recent designs have attempted to overcome these problems.Some attempt to alter the geometry of the stainless steel file in orderto provide more flexibility. This approach has had only limited success,and the stainless steel tools still have a tendency to break ifover-torqued or fatigued.

A series of comparative tests of endodontic instruments made ofnickel-titanium alloy (Nitinol™ or NiTi) and stainless steel wereconducted and published in an article entitled “An Initial Investigationof the Bending and the Torsional Properties of Nitinol Root CanalFiles,” Journal of Endodontics, Volume 14, No. 7, Jul. 1988, pages346-351. The Nitinol instruments involved in these tests weremanufactured in accordance with fabrication procedures and operatingparameters conventionally used in the machining of stainless steelendodontic instruments. This process involved grinding a helical flutein a tapered shaft to form helical cutting edges.

The reported tests demonstrated that the NiTi instruments produced bythe described machining process exhibited superior flexibility andtorsional properties as compared to stainless steel instruments, but thecutting edges of the instruments exhibited heavily deformed metaldeposits which, according to the article, rendered the instrumentsgenerally unsatisfactory for clinical use.

In general, alloys of nickel (Ni) and titanium (Ti) have a relativelylow modulus of elasticity (0.83 GPa) over a wide range, a relativelyhigh yield strength (0.195-690 MPa), and the unique and the unusualproperty of being “superelastic” over a limited temperature range.Superelasticity refers to the highly exaggerated elasticity, orspring-back, observed in many NiTi and other superelastic alloys over alimited temperature range. Such alloys can deliver over 15 times theelastic motion of a spring steel, i.e., withstand twisting or bending upto 15 times greater without permanent deformation The particularphysical and other properties of Nitinol alloys may be varied over awide range by adjusting the precise Ni/Ti ratio used. However, thesuperelastic properties of NiTi also make the material very difficultand expensive to machine.

Machining of NiTi tools for endodontic use has been an area ofsignificant development efforts in recent years. For example, U.S. Pat.No. 5,464,362 to Heath et. al. describes a method of grinding a rod of anickel-titanium alloy in order to create a fluted file. However, currentstate-of-the art manufacturing processes remain relatively expensive andslow and require sophisticated 6-axis grinding machines and the like.

Accordingly, there is a need for an improved endodontic file designwhich will allow for more economical manufacture of an endodontic toolfrom nickel titanium and other suitable alloys.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved endodontic file design and method of manufacturing such filesfrom nickel-titanium alloys, stainless steel and/or other materials. Itis another object of the invention to provide an endodontic instrumenthaving a reduced tendency to break during use. It is another object ofthe invention to improve the efficacy of an endodontic instrument and/orto reduce the number of instruments necessary to enlarge a root canal.Still another object of the invention is to provide an endodonticinstrument which can be quickly and economically manufactured usingconventional 3-axis grinding machines.

According to one embodiment of the present invention, a flutelessendodontic file is provided, formed from a generally prismatic rod(e.g., having multiple flats and interposed sharp corners) preferablytapered along its length. A plurality of notches are cut into theexposed corners in an alternating regular and/or irregular patterndefining cutting surfaces, points and/or edges. The notched cuttingsurfaces are formed such that the file, when rotated and/or reciprocatedwithin a root canal, effectively cuts/debrides hard tissue (known in theart as dentin) as well as soft tissue, thus, forming an optimal canalshape. The cutting surfaces are also preferably formed at an angle tothe centerline of the instrument to provide optimal cutting efficiencyand material removal. A dental instrument having features and advantagesof the present invention may be generally characterized as having aprismatic shape with multiple vertically aligned notched cuttingsurfaces preferably formed at an angle from the centerline of the shaft.The design exhibits increased flexibility and efficacy, has lesstendency to bind and break within the root canal and significantlyreduces manufacturing and capital equipment costs.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus summarized the general nature of the invention and itsessential features and advantages, certain preferred embodiments andmodifications thereof will become apparent to those skilled in the artfrom the detailed description herein having reference to the figuresthat follow, of which:

FIG. 1 is a section view of a tooth and root structure illustrating theuse of a conventional fluted endodontic instrument for performing atypical root canal procedure;

FIG. 2A is a side elevation view of a fluteless endodontic instrumenthaving features and advantages of the present invention;

FIG. 2B is a partial cross-section detail view of the fitting portion ofthe fluteless endodontic instrument of FIG. 2A;

FIG. 2C is a top plan view of the fitting portion of the flutelessendodontic instrument of FIG. 2A;

FIG. 2D is a detail view of the working portion of the flutelessendodontic instrument of FIG. 2A, illustrating multiple verticallyaligned notched cutting surfaces formed thereon;

FIG. 2E is a detail view of the distal portion of the flutelessendodontic instrument of FIG. 2A, illustrating the tip geometry thereof;

FIG. 2F is a bottom plan view of the working portion of the flutelessendodontic instrument of FIG. 2A;

FIG. 2G is a partial cross-section view of the working portion of thefluteless endodontic instrument of FIG. 2A;

FIG. 3A-C are time-sequenced isometric views illustrating one preferredmethod for manufacturing a fluteless endodontic instrument havingfeatures and advantages of the present invention; and

FIGS. 4A-H are schematic views of various alternative embodiments offluteless endodontic instruments having features and advantages of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a partial cross section of a tooth 50 and supporting rootstructure illustrating the use of a typical fluted endodontic file 80 tocarry out a standard root canal procedure. The root canal 56 of a toothhouses the circulatory and neural systems of the tooth. These enter thetooth at the terminus 52 of each of its roots 54 and extend through anarrow, tapered canal system to a pulp chamber 58 adjacent the crownportion 60 of the tooth. If this pulp tissue becomes diseased orinjured, it can cause severe pain and trauma to the tooth, sometimesnecessitating extraction of the tooth. Root canal therapy involvesremoving the diseased tissue from the canal 56 and sealing the canalsystem in its entirety. If successful, root canal therapy caneffectively alleviate the pain and trauma associated with the tooth sothat it need not be extracted.

To perform a root canal procedure, the endodontist first drills into thetooth 50 to locate the root canal(s) 56 and then uses an endodontic fileor reamer instrument 80 to remove the decayed, injured or dead tissuefrom the canal. These instruments are typically elongated cutting orabrading instruments which are rotated and/or reciprocated within theroot canal either by hand or using a slow speed drift. The primary goalis to remove all of the decayed or injured pulp tissue while leaving theintegrity of the central axis of the root canal relatively unaffected.Proper cleaning and shaping of the root canal 56 is important in orderto allow complete filling of the root canal void in a homogenous threedimensional manner such that leakage or communication between the rootcanal system and the surrounding and supporting tissues of the tooth 50is prevented. Once as much of the diseased material as practicable isremoved from the root canal, the canal 56 is sealed closed, typically byreciprocating and/or rotating a condenser instrument in the canal tourge a sealing material such as gutta-percha into the canal.

One of the primary challenges in performing root canal therapy is thatthe root canals are not necessarily straight and are often curved orconvoluted. Therefore, it is often difficult to clean the canal whilepreserving its natural shape. Many instruments (particularly the older,stainless steel instruments) have a tendency to straighten out the canalor to proceed straight into the root canal wall, altering the naturalshape of the canal. In some extreme cases, the instrument may transportcompletely through the canal wall causing additional trauma to the toothand/or surrounding tissues. Also, the openings of many root canals aresmall, particularly in older patients, due to calcified deposits on theroot canal inner walls. Thus the files or reamers must be able towithstand the torsional load necessary to penetrate and enlarge thecanal opening without breaking the instrument, as may also occasionallyoccur with the older stainless steel endodontic files.

To alleviate the transportation and breakage problems, highly flexibleendodontic files fabricated from nickel-titanium alloy (Nitinol™ orNiTi) were introduced and have become widely accepted. See, e.g. U.S.Pat. No. 5,882,198, incorporated herein by reference. But conventionalfluted instrument designs are difficult to manufacture from Nitinolalloys, often requiring expensive grinding operations and specialized6-axis grinding machines to create the desired continuous helicalfluting and sharp cutting edges. Conventional fluted instruments 80 alsosuffer from an occasional tendency to bind and/or to advanceunpredictably into the root canal 56 by virtue of a “screwing-in” effectas the instrument is rotated. In many cases, this binding or screwing-ineffect can result in the file breaking inside the canal. In the mostsevere cases, the fluted instrument 80 can actually drive itself throughthe terminus of the canal 56 and into the patient's jaw bone andsurrounding soft tissues.

FIGS. 2A-G illustrate one preferred embodiment of a fluteless endodonticfile having features and advantages of the present invention. The file100 generally comprises a shaft 110 having a shank portion 104 and anelongated working portion 106. The working portion 106 extends from aproximal end 107 adjacent the base of the shank 104 to a distal end 108terminating in a tip 150. The shank portion 104 preferably includes afitting portion 109 for mating with the chuck of a dental handpiece (notshown). The fitting portion 109 includes a generally I-shaped flat side182 which defines a step 184 and a generally semicircular disk 186 aboveand adjacent to a generally semi-circular groove 188. Such fitting 109is typical of those employed in the dental industry for connecting orinterfacing a dental tool with dental drill or handpiece.

Alternatively and/or in addition to the fitting portion 109, the shankportion 104 may include a knurled or otherwise treated surface (notshown) or handle to facilitate hand manipulation of the file 100. Thus,the instrument 100 may either be used by manipulating the instrumentmanually in a rotating or reciprocating action, or the instrument may bemanipulated by attaching the fitting portion 109 of the instrument to amotorized handpiece for effecting more rapid removal of tissue from theroot canal, as desired.

The working portion 106 of the instrument 100 preferably has a lengthranging from about 3 mm to about 18 mm. A standard length is about 16mm. The working portion 106 may have a constant cross-sectional diameteror, more preferably, it is tapered from the proximal end 107 to thedistal end 108, as shown. In the particular embodiment shown, the taperis substantially uniform—that is, the rate of taper is constant alongthe working portion 106. A preferred taper rate ranges from about 0.01mm/mm to about 0.12 mm/mm and may be constant or varied along the lengthof the working portion 106.

The shank 110 is preferably formed from a rod of nickel titanium alloy,such as SE508 nickel-titanium wire manufactured by Nitinol Devices andComponents, Inc. of Fremont, Calif. This is a typical binarynickel-titanium alloy used for endodontic files and comprises about 56%nickel and about 44% titanium by weight. Table 1, below, summarizescertain selected material properties of the SE508 NiTi alloy: TABLE 1SE508 MATERIAL PROPERTIES PHYSICAL PROPERTIES Melting Point 13102° C.Density 6.5 g/cm3 Electrical Resistivity 82 μohm-cm Modulus ofElasticity 75 × 10{circumflex over ( )}6 MPa Coefficient of ThermalExpansion 11 × 10-6/° C. MECHANICAL PROPERTIES Ultimate Tensile Strength(UTS) 1150 Mpa Total Elongation 10% SUPERELASTIC PROPERTIES LoadingPlateau Stress @ 3% strain  450 MPa Superelastic Strain (max)   8%Permanent Set (after 6% strain) 0.2% Transformation Temperature (Af)5-18° C. COMPOSITION Nickel (nominal) 55.8 wt. % Titanium (nominal) 44.2wt. % Oxygen (max) 0.05 wt. % (max) Carbon (max) 0.02 wt. % (max)

If desired, special heat treatments may be employed and/or traceelements of oxygen (O), nitrogen (N), iron (Fe), aluminum (Al), chromium(Cr), cobalt (Co) vanadium (V), zirconium (Zr) and/or copper (Cu), maybe added to achieve desired mechanical properties. See, for example,U.S. Pat. No. 5,843,244 to Pelton, incorporated herein by reference.While nickel-titanium alloys are preferred, the invention disclosedherein is not limited as such, but may be practiced using a wide varietyof other suitable alloys, including other super-elastic alloys andconventional medical-grade steel or nickel alloys.

The shaft 110 is preferably rolled, ground, extruded or otherwisemachined to produce an elongated prismatic structure having asubstantially constant or tapering geometric shape in cross-section. Asquare cross-section is particularly preferred, having four flat facingsurfaces (“flats”) 126 and four corners 124 (preferably sharp), asillustrated in FIG. 2G. Of course, those skilled in the art will readilyappreciate that a wide variety of other shapes may also be used withefficacy, such as triangular, hexagonal, octagonal rectangular, or otherregular polygon. Certain irregular polygons may also be used withefficacy such as those formed with one or more exposed corners and oneor more facing surfaces (flat or otherwise). Also, the shape can varyand/or alternate along the length of the instrument, as desired.

A plurality of notches 118 are formed along each corner 124 of the shaft110 defining cutting planes 130, cutting edges 128 and relief surfaces120. Notches 118 are preferably vertically aligned and formed in aregular spaced pattern 124 along each corner 124. Preferably, notches118 are registered relative to notches formed on adjacent corners suchthat as the instrument 100 is rotated clockwise each successive corner124 presents a notch 118 and a cutting plane 128 that is successivelyhigher and higher up the working portion 106 of the shank 104 fromdistal end 108 to the proximal end 107. Advantageously, in this mannerthe cutting edges 128 cut or abrade against the root canal wall,expanding the canal opening while successively urging removed anddislodged tissues upward out of the canal. Of course, those skilled inthe art will readily appreciate that various alternative notch patternsmay be employed, including forming notches 118 on alternating and/orselected corners 124 only, forming notches 118 in a regular or irregularspaced pattern on one or more selected corners 124, alternating thesize, spacing, angle and placement of notches 118 on selected corners124 to achieve any number of desired effects. Notches 118 may besubstantially uniform in depth or, more preferably, notches 118 increasein depth from the distal end 108 to the proximal end 107 to provideoptimal cutting and tissue removal as well as instrument flexibility.

If desired, notches 118 may be angled or otherwise formed to providecutting edges 128 with a desired rake angle. Thus, preferably thecutting planes 130 are formed at an angle α with respect to thelongitudinal axis of between about 60° and 120°, more preferably betweenabout 95° and 115° and most preferably about 105°. In an alternativeembodiment, the cutting planes 130 may be formed at an angle α withrespect to the longitudinal axis of between about 90° and 170°, morepreferably between about 110° and 160° and most preferably about 120°.The relief surface 120 is preferably formed at an angle β with respectto the longitudinal axis of between about 5° and 45°, more preferablybetween about 10° and 20° and most preferably about 15°. The reliefsurface 120 may also be formed at any desired angle ψ with respect to anadjacent flat surface 126. An angle ψ of about 45° is chosen in thepreferred embodiment illustrated in FIG. 2G. Of course, those skilled inthe art will appreciate how the particular notch geometries can bevaried to produce desired effects without departing from the essentialteachings disclosed herein.

The tip 150 of the instrument 100 may assume any number of a variety ofpossible configurations (e.g., chisel, cone, bullet, multi-facetedand/or the like), depending upon the preference of the endodontist andmanufacturing conveniences. In the illustrated embodiment, the tip 150is formed as a simple cone, as illustrated in FIGS. 2E and 2F. Theconical tip 150 preferably has an included cone angle γ of between about45° and 120°, more preferably between about 60° and 100° and mostpreferably about 75°. The surface of the tip 150 may be uninterruptedand/or one or more notches 118 may extend into the tip 150 to form oneor more additional cutting edges, as desired. Again, those skilled inthe art will readily appreciate how the particular geometries can bevaried without departing from the essential teachings disclosed herein.

Advantageously, the fluteless file 100 according to the preferredembodiment described above is highly efficacious in cleaning andexpanding root canal openings. The notches 118 and cutting surfaces 130formed thereby are more effective in scraping away and removing hard andsoft tissues from the root canal. The notched design also reducesfriction and improves the flexibility of the file for a given materialand cross-section, allowing larger diameter files to be used in highlycurved root canals. This improves the speed and efficacy of the rootcanal procedure and reduces the number of endodontic files and otherspecialized tools required to complete each procedure. The disclosedfile design is also significantly less expensive to manufacture thanconventional fluted files due to its relatively simple design and, mostnotably, the lack of helical flutes. The fluteless endodontic filedesign according to the above-described embodiment can be easily andexpeditiously fabricated from stainless steel or nickel-titanium alloysusing a standard 3-axis grinding machine with or without a rotatingchuck. Because comparatively little material need be removed in grindingthe file 100 from a tapered square or other prismatically-shaped blank,the overall grinding operation is significantly streamlined and requiresless redressing and replacing of worn grinding wheels. The lack ofhelical flutes also diminishes the possibility of canal transportationand eliminates the possibility of the file 100 advancing unpredictablyinto the root canal by virtue of a “screwing in” effect. If the tip 108were to bind or lodge in the canal, the working portion 106 of the file100 would twist, effectively forming a reverse helix and thereby urgingthe file out of the canal. Thus, the overall safety of the root canalprocedure is improved.

FIGS. 3A-C are time-sequenced schematic views illustrating one preferredmethod of manufacturing a fluteless endodontic instrument havingfeatures and advantages of the present invention. FIG. 3A shows atapered blank shaft 210 having a desired, generally prismatic shape—inthis case a square having four flats 226 and an equal number ofinterposed corners 224. The shaft preferably comprises a stainless steelor Nickel-Titanium alloy. The shaft 210 can be shaped from a length ofwire by rolling, extruding, grinding or other machining operations toreduce its cross-section and produce the desired tapered, generallyprismatic shape. If sharp edges are desired at corners 224, then a finalgrinding operation is preferably performed to achieve a smooth groundsurface on each flat 226. Of course, those skilled in the art willreadily appreciate that “flats” 226 may not necessarily be flat, but mayhave a rounded, curved, convex and/or concave features, as may bedesired. However flat surfaces are particular preferred formanufacturing expedience.

Once the blank 210 is suitably shaped, successive grinding operationsare preferably carried out using a rotating grinding wheel 250 to form aplurality of substantially vertically-aligned notches 218 on one or morecorners 224, as illustrated in FIG. 3B. These notches may be formedusing either high-speed or slow-speed grinding operations carried outusing a conventional 3-axis grinding machine in accordance withwell-documented grinding techniques. Any number of such notches 118 maybe formed in this manner, as desired.

The wheel 250 may be dressed, shaped and/or manipulated relative to thework piece in any suitable manner desired to produce correspondingground cutting surfaces 220 and 230, as illustrated. A flat grindingwheel 250 manipulated along a linear cutting path is particularlypreferred for manufacturing expedience. Preferably, the wheel 250 isinclined at an angle β with respect to the longitudinal axis of theshaft 210 to produce a desired inclination of recessed surfaces 220. Ofcourse, those skilled in the art will readily appreciate that otherspecialized shapes and/or more sophisticated wheel manipulationtechniques may be used to create rounded, radiused, and/or filletedsurfaces 230, 220, as desired. For example, the wheel 250 may besuitably dressed or radiused along one corner to produce a roundedsurface and/or filleted corner instead of the sharp recessed corners 225illustrated in FIG. 3B. The perimeter surface of the wheel 250 may bedressed square with the facing surface or it may be angled, as desired.

Preferably, the grinding wheel 250 is moved past the work piece 210 (orvice-versa) in such a manner that notches 218 are formed with a slopedcutting surface 230 producing an angle α₁ of between about 50° and 110°,more preferably between about 70° and 90°, and most preferably about 80°with respect to the longitudinal axis of the shaft 210, as indicated inFIGS. 3B, 3C. IN an alternative preferred embodiment, the grinding wheel250 is moved past the work piece 210 (or vice-versa) in such a mannerthat notches 218 are formed with a sloped cutting surface 230 producingan angle α₁ of between about 20° and 110°, more preferably between about25° and 80°, and most preferably about 60° with respect to thelongitudinal axis of the shaft 210 If desired, additional notches 218′may be formed with sloped cutting surfaces 230′ having an angle α₂ ofbetween about 70° and 130°, more preferably between about 90° and 110°,and most preferably about 100° with respect to the longitudinal axis ofthe shaft 210, as indicated in FIG. 3C. In this manner, the flutelessinstrument 200 is equally effective when rotated in either a clockwiseor counterclockwise direction, with or without reciprocation. Of course,those skilled in the art will readily appreciate that the particularnumber, placement and geometries of the notches 218, 218′ and theresulting exposed cutting surfaces 220, 220′, 230, 230′ may be variedwithout departing from the scope and spirit of the invention disclosedherein.

FIGS. 4A-H are schematic views of various alternative embodiments offluteless endodontic instruments having features and advantages of thepresent invention. FIG. 4A is a simplified schematic cross-sectionrepresentation of a fluteless endodontic file having a symmetricaltriangular cross-section with notches (hidden lines) and resultingcutting surfaces formed along the three exposed corners thereof FIG. 4Bis a simplified schematic cross-section representation of a flutelessendodontic file having a symmetrical hexagonal cross-section withnotches (hidden lines) and resulting cutting surfaces formed along thesix exposed corners thereof FIG. 4C is a simplified schematiccross-section representation of a fluteless endodontic file having asymmetrical “star-shaped” cross-section with notches (hidden lines) andresulting cutting surfaces formed along the six exposed corners thereofFIG. 4D is a simplified schematic cross-section representation of afluteless endodontic file having a symmetrical square cross-section withconcave flats and acute corners and with notches (hidden lines) andresulting cutting surfaces formed along the four exposed cornersthereof. FIG. 4E is a simplified schematic cross-section representationof a fluteless endodontic file having a rectangular cross-section withnotches (hidden lines) and resulting cutting surfaces formed along twoof the exposed corners thereof FIG. 4F is a simplified schematiccross-section representation of a fluteless endodontic file having afrusto-cylindrical cross-section with concave and convex side surfacesdefining four corners and notches (hidden lines) and resulting cuttingsurfaces formed along two of the exposed corners thereof FIG. 4G is asimplified schematic cross-section representation of a flutelessendodontic file having an asymmetrical polygonal cross-section withnotches (hidden lines) and resulting cutting surfaces formed along twoof the exposed corners thereof FIG. 4H is a simplified schematiccross-section representation of a fluteless endodontic file having adiamond-shaped cross-section with notches (hidden lines) and resultingcutting surfaces formed along the two outer-most exposed cornersthereof.

The concepts and teachings of the present invention are particularlyapplicable to nickel-titanium alloys and endodontic instruments (files,reamers, obturators, drill bits and the like) fabricated therefrom.However, the invention disclosed herein is not limited specifically toendodontic instruments fabricated from NiTi alloys, but may be practicedwith a variety of dental instruments using any one of a number of othersuitable medical-grade alloys. Although this invention has beendisclosed in the context of certain preferred embodiments and examples,it will be understood by those skilled in the art that the presentinvention extends beyond the specifically disclosed embodiments to otheralternative embodiments and/or uses of the invention and obviousmodifications and equivalents thereof Thus, it is intended that thescope of the present invention herein disclosed should not be limited bythe particular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

1. An endodontic instrument for cleaning and extirpating the walls of aroot canal, said instrument comprising: an elongated shaft having agenerally prismatic shape defined by three or more sides and three ormore exposed corners; and a plurality of notches formed along at leastone of said corners, said notches defining one or more cutting planeshaving cutting edges adapted to contact the walls of said root canalwhen said instrument is rotated and/or reciprocated therein.
 2. Theendodontic instrument of claim 1 wherein said elongated shaft is taperedalong its length.
 3. The endodontic instrument of claim 2 wherein saidelongated shaft has a varying taper rate along its length.
 4. Theendodontic instrument of claim 1 wherein said three or more sides andthree or more exposed corners are generally straight.
 5. The endodonticinstrument of claim 1 wherein said three or more sides and three or moreexposed corners are generally curved or twisted.
 6. The endodonticinstrument of claim 1 wherein one or more of said three or more sidesare characterized by a flat, convex or concave surface.
 7. Theendodontic instrument of claim I wherein said shaft comprises a medicalgrade alloy.
 8. The endodontic instrument of claim 1 wherein said shaftcomprises a medical grade alloy including approximately 56% nickel and44% titanium by weight.
 9. The endodontic instrument of claim 1 whereinsaid shaft has a cross section comprising a regular or irregularpolygon.
 10. The endodontic instrument of claim 1 wherein said shaft hasa cross section comprising one or more of the following shapes: square,triangular hexagonal octagonal, rectangular, trapezoidal, star-shaped ordiamond-shaped.
 11. The endodontic instrument of claim 1 wherein saidshaft has a varying cross section shape along its length.
 12. Theendodontic instrument of claim 11 wherein said shaft varies from agenerally octagonal cross section at a proximal end thereof tapering tosquare cross section at a distal end thereof.
 13. The endodonticinstrument of claim 11 wherein said notches vary in depth from aproximal to a distal end of said shaft.
 14. The endodontic instrument ofclaim 1 wherein said cutting planes are formed such that the file, whenrotated and/or reciprocated within a root canal, effectivelycuts/debrides hard tissue.
 15. The endodontic instrument of claim 1wherein said cutting planes are formed at an angle α from the centerlineof said shaft of between about 110° and 160°.
 16. The endodonticinstrument of claim 1 wherein said cutting planes are formed at an angleα from the centerline of said shaft of between about 90° and 170°. 17.The endodontic instrument of claim 1 wherein said cutting planes areformed at an angle of about 120° from the centerline of said shaft. 18.The endodontic instrument of claim 1 wherein said cutting planes areformed at alternating angles of 120° and −120° from the centerline ofsaid shaft.
 19. The endodontic instrument of claim 1 wherein one or moreof said notches further define relief surfaces formed at an angle β withrespect to the longitudinal axis of between about 5° and 45°.
 20. Theendodontic instrument of claim 1 wherein said notches are registeredrelative to notches formed on adjacent corners such that as theinstrument is rotated clockwise each successive corner presents acutting plane that is successively higher and higher up the workingportion from a distal end to a proximal end thereof.
 21. An endodonticinstrument for cleaning and extirpating a root canal, comprising: anelongated shaft having a working portion extending from a proximal endto a distal end, said working portion having multiple sides and multipleinterposed corners generally defining the intersection of said multiplesides; and multiple recessed notches formed along at least one of saidcorners, said notches defining exposed cutting surfaces with cuttingedges adapted to contact the walls of said root canal when saidinstrument is either rotated and/or reciprocated therein.
 22. Theendodontic instrument of claim 21 wherein said elongated shaft istapered along its length from said proximal to said distal end.
 23. Theendodontic instrument of claim 22 wherein said elongated shaft has avarying taper rate along its length.
 24. The endodontic instrument ofclaim 21 wherein three or more sides and three or more interposedcorners are generally straight extending from said proximal to saiddistal end of said elongated shaft.
 25. The endodontic instrument ofclaim 21 wherein three or more sides and/or three or more exposedcorners are generally curved or twisted from said proximal to saiddistal end of said elongated shaft.
 26. The endodontic instrument ofclaim 21 wherein one or more of said sides are characterized by a flat,convex or concave surface.
 27. The endodontic instrument of claim 21wherein said shaft comprises a medical grade alloy.
 28. The endodonticinstrument of claim 21 wherein said shaft comprises a medical gradealloy including approximately 56% nickel and 44% titanium by weight. 29.The endodontic instrument of claim 21 wherein said shaft has a crosssection comprising a regular or irregular polygon.
 30. The endodonticinstrument of claim 21 wherein said shaft has a cross section comprisingone or more of the following shapes: square, triangular hexagonaloctagonal, rectangular, trapezoidal, star-shaped or diamond-shaped. 31.The endodontic instrument of claim 21 wherein said shaft has a varyingcross sectional shape along its length.
 32. The endodontic instrument ofclaim 21 wherein said notches vary in depth from the proximal to thedistal end of said shaft.
 33. The endodontic instrument of claim 21wherein said cutting surfaces are formed such that the file, whenrotated and/or reciprocated within a root canal, effectivelycuts/debrides hard tissue.
 34. The endodontic instrument of claim 31wherein said cutting surfaces are formed at an angle α from thecenterline of said shaft of between about 110° and 160°.
 35. Theendodontic instrument of claim 21 wherein said cutting surfaces areformed at alternating angles of 120° and −120° from the centerline ofsaid shaft.
 36. A method for fabricating an endodontic instrument forcleaning and extirpating a root canal, comprising: selecting anelongated shaft of material having multiple side surfaces and multipleinterposed corners; and forming multiple recesses in a spaced oralternating regular or irregular pattern along at least one of saidcorners, said recesses defining exposed cutting surfaces adapted tocontact the walls of said root canal when said instrument is rotatedand/or reciprocated therein.
 37. The method of claim 36 wherein saidelongated shaft is selected or formed to have a taper along its length.38. The method of claim 36 wherein said elongated shaft is selected tohave a varying taper rate along its length.
 39. The method of claim 36wherein said elongated shaft is selected or formed to have three or moreside surfaces and three or more interposed corners and wherein said sidesurfaces and said corners are generally straight.
 40. The method ofclaim 36 wherein said elongated shaft is selected or formed to havethree or more sides and three or more exposed corners and wherein saidside surfaces and said corners are generally curved or twisted.
 41. Themethod of claim 36 wherein said elongated shaft is selected or formedfrom a medical grade alloy including approximately 56% nickel and 44%titanium by weight.
 42. The method of claim 36 wherein said multiplerecesses are formed using a grinding wheel.
 43. The method of claim 36wherein said multiple recesses are formed using a grinding wheelassociated with a grinding machine having no more than 3-axis motion.44. The method of claim 36 wherein said multiple recesses are formedwith varying depth from the proximal to the distal end of said shaft.45. The method of claim 36 wherein said cutting surfaces are formed suchthat the file, when rotated and/or reciprocated within a root canal,effectively cuts/debrides hard tissue.
 46. The method of claim 36wherein said cutting surfaces are formed at an angle α from thecenterline of said shaft of between about 110° and 160°.
 47. The methodof claim 36 wherein said cutting surfaces are formed at alternatingangles of 120° and −120° from the centerline of said shaft.